The human body is a hostile environment to implanted medical devices and materials, particularly to chronically implanted electrical cables and leads. For example, implantable cardiac cables are typically coupled at their proximal ends with implanted pacemaker and pacemaker/cardioverter/defibrillator pulse generators. Over the years of implantation, the cables and insulation are subjected to cumulative mechanical stresses that can result in degradation of the insulation or fractures of the lead conductors with untoward effects on device performance and patient well-being.
The traditional tubular insulation is most commonly composed of an elastomeric material such as silicone or polyurethane. The combination of a helically wound conductor with elastomeric outer insulation provides conventional construction with the potential for a substantial amount of elastic deformation in the direction of the length of the lead.
An implantable electrical cable must also be completely biocompatible, in that the exterior of the cable is preferably made of biocompatible materials which are strong and flexible enough that the constant flexure caused by movement of the patient or his organs does not cause the cable to rupture. The exterior of the cable is also preferably smooth to avoid abrasion of surrounding tissue and other discomfort to the patient. The cable is also preferably compliant and supple, to avoid damage to surrounding tissue by being so stiff that it resists movement as the surrounding tissues move. A stiff and inflexible cable would apply a bias force, which would resist movement of the patient, and which would cause discomfort to the patient.
U.S. Pat. No. 4,000,745 discloses the electrical leads for cardiac stimulators comprising an insulated electrical conductive section and a lead-in securing section including a helical member which may be screwed into the heart muscle.
U.S. Pat. No. 6,374,141 discloses a bioelectrical stimulus cable in which the insulated electrical lead includes at least one fibril having a coating of rigid insulating, low friction material. A coating of shock dampening elastomeric, insulating material is tightly set about the rigid, insulating, low friction material. In one preferred embodiment, the cable includes a braided sheath encompassing a portion of the cable and increasing the tensile strength of the cable.
Notwithstanding the variety of the implantable cable designs that have been proposed, there is still a desire to improve the mechanical characteristics and the product capability of the implantable electrical cables.
An implantable cable is preferably thin. Cables that have many wires will become stiffer as the numbers of parallel conductors increases. A cable should be readily interconnectable with other devices, that is, having a grouping or arrangement of conductors that are dimensionally controlled and predictably located for reliable fastening to other devices.
It is thus an object of the present invention to provide an implantable cable which can withstand constant flexure during long term chronic implantation.
A still further object of the present invention is to provide an implantable cable which is encased with fluoropolymer such as FEP or PFA
A further object of the present invention is to provide an implantable cable having improved mechanical characteristics and improved manufacturability.
A still further object of the invention is to provide a manufacturing process for an implantable cable which can be manufactured in a simple and reliable way.
These and other objects of the invention will be appreciated by reference to the summary of the invention and to the detailed description of the preferred embodiment that follow. It will be appreciated that all of the foregoing objectives may not be satisfied simultaneously by the preferred embodiment or by each of the claims.